Unless you have a loose or cracked fuel line or bad wiring connection causing the pump to not run or loose pressure my best educated guess would be that you didnt change the fuel filter when you replaced the pump in which case if the filter is plugged all of your pressure would be on the fuel tank side of the filter causing you to have little or no pressure at the test port on the fuel rail.
I would try replacing the fuel pressure regulator. That was my problem.
check the oil level in the hpop.
There are several possibilities. The 2 most common would be the water heater needs replacing, or you need a repipe.
A thermostat that was stuck then suddenly became unstuck might do that. If the coolant level and the rest of the cooling system seem OK, try replacing the thermostat.
fuel filter? fuel lines? what all have you checked.
bad check valve or a leak.
The pressure from the radiator is pushing out through the overflow canister. Probably solved with new radiator cap but could be an indication of head gasket problems if pressure gets too high.
I would start with replacing the fuel filter. Also they are bad about fuel leaks from the fuel pressure regulator.
The trans mission IS probably going out. This is a well know defect in the 2002 Tahoe. Google it.
driving it to roughly
bad or failing alternator
Type your answer here... I had the same problem with my 96 Tahoe.. Vortec 350. Problem was a blown intake gasket.